Process for the preparation of acrylic end-products for external use

ABSTRACT

A process is described for the preparation of end-products made of acrylic fiber, for external use, by the joining of one or more sheets with a copolyamide adhesive, resistant to solar light, the above junction been effected by the melting of said adhesive on the acrylic matrix and subsequent pressing of the glued area with a system capable of exerting an adequate pressure.

[0001] The present invention relates to a process for the preparation ofend-products for external use, made of acrylic fibre, which uses acopolyamide adhesive resistant to solar light.

[0002] Covers or sun shields, such as for example external awnings, arepreferably made of acrylic fibre, either raw or dyed with pigments,which are extremely stable to solar radiation.

[0003] Preference for the use of acrylic fibre for the preparation ofend-products exposed to the sun is due to the exceptional resistance ofthis fibre to solar radiation.

[0004] Whereas other fibres such as those deriving from polypropylene,cotton, polyester, etc., undergo a considerable deterioration intoughness after a few months of exposure to light, acrylic fibres remainunaltered and maintain almost all of their initial toughness afterseveral years of exposure.

[0005] Pigments can be incorporated into acrylic fibres, which, ifsuitably selected, enable the mechanical resistance and the originalbrightness of the colours of the fibres to remain unaltered.

[0006] In order to produce end-products for external use having thedesired dimensions, it is necessary to join sheets of acrylic fibre.This operation is typically effected with traditional seaming systemsusing threads of various materials, preferably of polyester orpolyamide.

[0007] This system however, in addition to having a limited durationover a period of time for the parts of sewing threads exposed to solarradiation, also presents the problem of costs and thickness of thejunctions.

[0008] The borders of the sewn sheets are, in fact, folded inwards andthis increases the thickness of the sewn parts increasing the bulk whenthe awning is rolled up.

[0009] Under conditions of humidity or water absorption, the rolled-upawning is subject to greater stress on the area of the junctions and, asa result of the heat deriving from solar radiation, produces permanentand visible deformations, when the awning is unrolled, in the form ofunaesthetic undulations.

[0010] For these reasons, a system has been studied for joining theborders of the sheets by means of adhesives.

[0011] Adhesives consisting of polyacrylates, synthetic rubbers, vinylpolymers, polyesters, polyurethanes, etc., are generally used, appliedalone or with organic solvents.

[0012] These joining systems however have proved to be difficult toeffect for the following reasons:

[0013] 1. the use of organic solvents such as toluene, chlorinatedhydrocarbons, acetone, etc. requires, during processing, the use ofaspiration systems to limit their toxicity and can also give rise tofires, explosions, etc.

[0014] 2. these adhesives have a lower mechanical resistance than thatobtained with the traditional seaming system and they are not stable tosolar exposure or weather-proof.

[0015] It has now been found, according to the present invention, thatit is possible to overcome the drawbacks of the known art discussedabove, by using a copolyamide adhesive for joining the borders ofacrylic cloth. The use of this adhesive provides substantial advantages,in particular:

[0016] 1. a mechanical resistance equal to or higher than that oftraditional seaming systems;

[0017] 2. a high resistance to light in terms of yellowing resistanceand conservation of toughness;

[0018] 3. a high physico-chemical affinity for the acrylic fibre whichallows perfect wettability of the surface of the end-product, on thepart of the adhesive, which results in the exceptional tensile strengthof the junctions.

[0019] In accordance with this, the objective of the present inventionrelates to a process for the preparation of end-products for externaluse which comprises the joining of one or more sheets made of fabricessentially consisting of acrylic fibres by means of a copolyamideadhesive, the above junction being effected by applying said adhesive tothe acrylic matrix by melting, with subsequent pressing in the gluedarea by means of a system capable of exerting an adequate pressure.

[0020] Copolyamide adhesives suitable for the purposes of the presentinvention are preferably selected from those consisting of a polyamideterpolymer based on 6/6.6/12 nylon and have the followingcharacteristics:

[0021] melting point ranging from 115-130° C.;

[0022] glass transition temperature ranging from 15 to 20° C.;

[0023] viscosity of the molten product at 2.16 kg/160° C. ranging from150 to 700 Pa.s.

[0024] These adhesives can be prepared with the known techniques and arealso commercially available.

[0025] The adhesive, in powder form, can be used in aqueous dispersionin the form of a spreadable paste and is applied to the edge of one ofthe two sheets with subsequent pressing and melting of the adhesive byheating to about 150° C.

[0026] Alternatively, the adhesive in powder form is fed to a deviceheated to the melting point of the polymers and is spread, in a finelayer, on the edge of the fabric.

[0027] As the molten adhesive is applied on a layer of the fabric, theedge of the other sheet of fabric is overlapped, exerting a pressurewhich is sufficient to allow adhesion of the borders of the fabric.

[0028] For this purpose, calenders, flat plates or other devices capableof exerting adequate pressure, can be used.

[0029] The end-products for external use obtained using these adhesiveshave proved to be more resistant than those obtained using adhesiveswith a greater nominal mechanical resistance, for example adhesivesbased on copolyesters, but with a poor affinity with the acrylic fibre.

[0030] For these end-products, the thickness in the overlapping area ofthe edges is the sum of the thicknesses of the single sheets in additionto a negligible thickness of the molten adhesive. The width of theoverlapping area of the two sheets glued by the copolyamide adhesive isin relation to the adhesion strength required.

[0031] The following examples are illustrative but do not limit thescope of the invention described.

EXAMPLES 1-11

[0032] Rectangular sheets of 20 cm×28 cm, with the long side parallel tothe warp direction, were cut from an acrylic fibre fabric of 290 g/m².

[0033] The edges of the sheets of fabric were joined by applying theadhesive with a device consisting of a motorized screw extruderelectrically heated to a temperature of 180° C., in which the adhesiveproducts in powder form were fed from one end, whereas the other end ofthe extruder consisted of a tube having a diameter of 1 cm forming adownward angle and terminating with a flat spout having a 2 cm slit,suitable for spreading a thin layer of molten adhesive onto the edge ofthe fabric.

[0034] As the molten adhesive was spread onto one side of the fabric,the edge of the other sheet of fabric was overlapped, and an adequatepressure exerted by means of two chromium plated rolls which caused thetwo sheets of fabric to advance.

[0035] The following adhesives, in powder form, of EMS Chemie(Switzerland) were used in the experiments:

[0036] 1. copolyamide adhesive Griltex 2 (Sample A)

[0037] 2. copolyamide adhesive Griltex D1641A (Sample B)

[0038] 3. copolyester adhesive Griltex D1539E (Control Sample C)

[0039] 4. copolyester adhesive Griltex D1442E (Control Sample D)

[0040] All the samples were subjected to tensile strength testsaccording to the procedures indicated by the methods ASTM D1682 (testmethod for breaking load and elongation of fabrics) and ASTM D1683(standard test method for seams in shuttle fabrics).

[0041] The tensile tests were effected according to two modes:

[0042] (I) in a tangent direction to the junction plane;

[0043] (II) in a perpendicular direction to the junction plane with thelifting of one of the joining edges.

[0044] The tensile tests were compared with the resistance of the fabricwithout junctions (E) and with two edges of fabric joined by atraditional seaming system with polyester thread (F).

[0045] The adhesives were subsequently evaluated with tensile tests at0° C. and at 50° C. and after exposure to the Xenotest under stormconditions for 1000 hours, equivalent to 1 year of exposure to sun andstorms.

[0046] The results are summarized in Table 1 below. TABLE 1 Breakingload in N/2 cm Tensile Room Sample mode temperature 0° C. 50° C.Xenotest E (I) 430 420 360 — F (I) 410 n.d. n.d 337 F (II)  40 n.d. n.dn.d. A (I) > fabric > fabric = fabric > fabric A (II)  45  47  40 n.d. B(I) > fabric > fabric = fabric = fabric B (II)  40  40  38 n.d. C (I)300 320 250 150 C (II)  5  6  4 n.d. D (I) 280 290 220 140 D (II)  7  7 5 n.d.

[0047] >fabric means that the fabric breaks but not the glued part;=fabric means that at times the fabric breaks and at times the gluedpart breaks.

[0048] n.d.=not determined.

[0049] From the results indicated in the table, it can be observed thatthe end-products glued with adhesives based on copolyamides haveperformances equal to or higher than traditional seams; end-productsglued with polymers based on copolyester have lower performances thantraditional seams.

1. A process for the preparation of end-products for external use whichcomprises joining one or more sheets made of fabric essentiallyconsisting of acrylic fibres by means of a copolyamide adhesive selectedfrom those based on 6/6.6/12 nylon, the above junction being effected bymelting said adhesive on the polymeric matrix.
 2. The process accordingto claim 1, wherein the sheets of fabric can be made of either raw orpigmented acrylic fibre.
 3. The process according to claim 1, whereinthe copolyamide adhesive has a melting point ranging from 115° C. to130° C. and a viscosity of the molten product at 2.16 kg/160° C. rangingfrom 150 to 700 Pa.s.
 4. The process according to claim 1, wherein thejoining of the sheets by means of the copolyamide adhesive is effectedby the melting of the adhesive with an extrusion system heated to180-200° C.
 5. The process according to claim 1, wherein, after thespreading of the molten copolyamide adhesive onto the edge of a firstsheet, the edge of the second sheet is overlapped with subsequentpressing of the glued area with a system capable of exerting an adequatepressure.
 6. The process according to claim 5, wherein the systemcapable of exerting the pressure is a calender or flat plate system. 7.The process according to claim 1, wherein the copolyamide adhesive inpowder form is in aqueous dispersion in the form of a spreadable pasteand is applied to the edge of one of the two sheets with subsequentpressing and melting of the polymer by heating to about 150° C.
 8. Theprocess according to claim 1, wherein the end-products are covers orsun-shields such as external awnings.
 9. The process according to claim1, wherein the thickness of the overlapping area of the sheets is thesum of the thicknesses of the single sheets in addition to a negligiblethickness of the molten copolyamide adhesive.
 10. The process accordingto claim 1, wherein the width of the overlapping area of the two sheetsglued by the copolyamide adhesive is in relation to the adhesionstrength required.